1. Field of the Invention
The invention relates to magnetic resonance imaging method for generating separate fat and water images of at least one slice where a plurality of sequences act on the slice in the presence of a steady magnetic field, each sequence comprising at least one first RF pulse which is followed by a phase encoding gradient as well as a magnetic gradient during which the spin resonance signal generated in the slice is detected, groups of sequences being formed with a position in time of the measuring gradient and/or a further RF pulse if any, which differs from one group to another, the number of sequences per slice being twice as large as necessary to generate a similar image without fat/water separation.
2. Description of the Related Art
The invention further relates to a magnetic resonance apparatus. A method of this kind is known from an article by Dixon in the magazine "Radiology", Vol. 153 (1984), pp. 189-194. A version which requires only one RF pulse per sequence is disclosed in EP-A 224 310, which corresponds to commonly owned U.S. Pat. No. 4,818,941. The known methods have a common aspect in that each sequence is repeated once, merely the distance in time between the RF pulses of the sequence or the distance in time between the single RF pulse and the measuring gradient being varied. Thus, two groups of sequences are formed. The number of sequences in each group corresponds to the number (N) of pixels in the direction of the phase encoding gradient for the images (fat or water) to be generated. The spin resonance signals from the two groups, occurring each time for the same phase encoding gradient, differ merely in that one of the components to be separated, for example the fat component, for one signal has a phase position which opposes that for the other spin resonance signal. Therefore, separate fat and water images can be generated in that either first the two groups of sequences are subjected to a respective two-dimensional Fourier transformation, the slice images thus produced being subtracted, or in that first the difference between the spin resonance signals obtained with the same phase encoding gradient is formed, the difference signals thus obtained being subjected to a two-dimensional Fourier transformation.